The regulation of microsomal HMG-CoA reductase, the rate controlling enzyme for cholesterol synthesis, and cholesterol 7 gamma- hydroxylase, the rate controlling enzyme for bile acid synthesis will be studied in normal liver, primary hepatocellular carcinomas, and hyperplastic hepatocellular nodules. By studying both enzymes under a variety of conditions designed to perturb bile acid and cholesterol synthesis, it should be possible to learn how the two synthetic processes are normally integrated and also to determine now this integration is deranged in hepatocellular neoplasms. This study could help to provide an explanation for the loss of dietary cholesterol mediated "feedback control" of cholesterol synthesis that has been reported in hepatocellular carcinomas.